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The goal for this task is to have a 7 segment display output my last name the first two initials of my first name. The output should be FURMANHE with F being the 000 state and 111 being the E state. The circuit performs this function, except the 7 segment display, when powered up, starts with E instead of F. The circuit then counts upward as normal, rotating through U R M A N H and E again. So to reiterate and be clear, the circuit a)counts up sucessfully, b) displays all characters as they're intended to be displayed. But, the characters start from the end of my name instead of the first letter in my name.

I have fiddled with the circuit some, and done some more research on the pinouts of the jk flip flops. I thought perhaps inverting the preset or clear pins, or removing them altogether may help. They did not. I tried setting the output of each JK flip flop to !Q instead of Q. This produced the desired result in Multisim, but I can't replicate this on the actual breadboard. In multisim, using !Q, the circuit sucessfully counts from 000 (F) but on the breadboard, counting starts at H instead of E.

I am looking through the data sheet, but could the issue with !Q not working on the breadboard be related to some physical property of my real world flip flops?

Here is a pic of the circuit in Multisim: Multisim Export

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  • \$\begingroup\$ It appears everything is working properly however I do not understand how you get it to the 00 state? Is the reset portion missing? \$\endgroup\$
    – Gil
    Jun 19, 2021 at 21:57
  • \$\begingroup\$ Another user pointed to the reset portion. I think my flip flop design may be old or obsolete. Mine doesnt have a reset pin, it has preset and clear. Although, perhaps preset and clear are synonymous with reset-direct and set-direct (what I see on a schematic for a different manufacturer's flip flop). I am trying to look up more information on how to add the reset circuit. \$\endgroup\$ Jun 19, 2021 at 22:16
  • \$\begingroup\$ @SugarCereal191126 Without looking over your design for errors (assuming you have a reasonable design as using a ripple counter bugs me, but I won't worry about it), you should include a power-on reset. This can be as simple as a RC + a schmitt trigger gate. You may want to use this to synchronously enable your 555 output, as well, though. Yet more trouble. Wire it either to clear or preset depending on what you want for the initial state. If this is on a breadboard, make sure all your wiring is solidly in place. \$\endgroup\$
    – jonk
    Jun 19, 2021 at 22:37
  • \$\begingroup\$ @SugarCereal191126 In fact, this kind of circuit just begs for a nice clocking circuit that can be operated manually (push button) or at varying speeds with a 555 or at selected fixed speeds using crystals. It should include a nice power-on reset with a sharp, clean behavior that can also be manually triggered. If you get that solved, you'll have something very reliable and usable for all your clocking-future needs. \$\endgroup\$
    – jonk
    Jun 19, 2021 at 22:39
  • \$\begingroup\$ Using Qbar will invert your counter direction \$\endgroup\$ Jun 20, 2021 at 2:56

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except the 7 segment display, when powered up, starts with E instead of F.

I don't see a power-up reset circuit for your 74LS76's.

Have a look at this question for a solution using an R-C circuit:

How to initiate Preset and Clear in a JK flip flop?

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  • \$\begingroup\$ Thanks for the link. I added a RC circuit as described, with a 10k resistor and a 100uF cap. The "E" is still showing up, but it flashes for half a second or less, instead of displaying for a full second or so. This seems to have helped, but it hasn't completly eliminated the problem. I also tried some other POR circuit designs (I dont fully understand the construction of them; Ive been copying what I've been seeing and tweaking the resistors/capacitors). The best example was a NAND gate tied to a pushbutton and a resistor to ground. When the pushbutton is pressed, the circuit restarts from F \$\endgroup\$ Jun 22, 2021 at 17:05
  • \$\begingroup\$ For POR you don't need such a large time constant. Try for R*C = 1 microsecond. You could even go for a lower time like 50 nanoseconds. \$\endgroup\$
    – ErikR
    Jun 22, 2021 at 17:18

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